1. Field of the Invention
The present invention relates to a method for manufacturing a stator core for a dynamoelectric machine such as an automotive alternator, for example, and particularly to a method for manufacturing a stator core formed by laminating a press-formed magnetic steel sheet material.
2. Description of the Related Art
FIG. 8 is a plan explaining a process for forming a laminated body by a first sheet in a conventional stator for an automotive alternator described in Japanese Patent Laid-Open No. 2001-112197 (Gazette), for example, FIG. 9 is a cross section taken along line IX-IX in FIG. 8 viewed from the direction of the arrows, FIG. 10 is a plan showing a second sheet in the conventional stator for an automotive alternator, FIG. 11 is a cross section taken along line XI-XI in FIG. 10 viewed from the direction of the arrows, FIG. 12 is an exploded perspective showing a process for inserting conductor segments into a stator core in the conventional stator for an automotive alternator, and FIG. 13 is a partial cross section explaining a mounted state of a stator winding in the conventional stator for an automotive alternator.
A conventional stator 1 is constituted by: a cylindrical stator core 2 in which slots 3 are formed at a predetermined pitch in a circumferential direction so as to open onto an inner circumferential side; a stator winding 4 installed in the slots 3 of the stator core 2; and insulators 5 mounted inside each of the slots 3.
The stator core 2 is provided with: a laminated body 7 constituted by a first sheet 6; and second sheets 8 disposed at first and second axial ends of the laminated body 7.
As shown in FIG. 8, the laminated body 7 is formed into a cylindrical shape by winding up the first sheet 6 for a predetermined number of winds into a helical shape, the first sheet 6 being formed by using a press die to punch recess portions 6a at a predetermined pitch in a strip-shaped magnetic steel sheet material. Here, the recess portions 6a are superposed in an axial direction of the laminated body 7, constituting first slot portions 3a. In the laminated body 7, the first sheet 6 is laminated with the press punch direction aligned, as shown in FIG. 9, and burrs 6b extending in the press punch direction remain on each layer of the first sheet 6 on inner wall surfaces of the first slot portions 3a. 
As shown in FIG. 10, the second sheets 8 are each formed into an annular shape by using a press die to punch a flat sheet composed of a magnetic steel sheet material having a sheet thickness greater than that of the first sheet 6. Here, second slot portions 3b corresponding in position to the first slot portions 3a are simultaneously press-formed. As shown in FIG. 11, chamfered portions 8a are formed on edge portions of the second slot portions 3b on a first end side of the second sheets 8. Moreover, the second sheets 8 are formed so as to be equal in diameter to the laminated body 7.
The second sheets 8 are disposed at first and second end surfaces of the laminated body 7 such that the positions of the first slot portions 3a and the second slot portions 3b align and the chamfered portions 8a face away from the laminated body 7, and the stator core 2 is prepared by applying several strips of laser welding so as to extend in an axial direction from a first end portion to a second end portion on the outer circumferential surfaces thereof. Moreover, the first and second slot portions 3a and 3b align in an axial direction, constituting the slots 3.
As shown in FIGS. 12 and 13, the stator winding 4 is constructed using a plurality of conductor segments 9 by joining together end portions of the conductor segments 9 by a joining method such as welding, etc. The conductor segments 9 are each prepared by bending into a U shape a short length of copper wire having an electrically-insulating coating. Here, large and small first and second conductor segments 9a and 9b form a basic unit and a plurality of these units are used. The conductor segments 9 are housed in the slots 3 so as to be surrounded by the insulators 5 such that the insulators 5 are interposed between the conductor segments 9 and inner wall surfaces of the slots 3. Together with the electrically-insulating coating covering the copper wire of the conductor segments 9, these insulators 5 ensure electrical insulation between the conductor segments 9 and the stator core 2.
The conductor segments 9 and the insulators 5 are inserted into the slots 3 of the stator core 2 in a direction aligned with the press punch direction of the first sheet 6, in other words, from top to bottom in FIG. 13. The stator winding 4 is prepared by bending first end portions of the conductor segments 9 extending outward from the slots 3 of the stator core 2 as indicated by the arrow in FIG. 13 and joining the first end portions to second end portions of conductor segments 9 separated by a predetermined pitch.
In the conventional stator 1 constructed in this manner, because the second sheets 8 having a thick sheet thickness are disposed on the first and second axial end portions of the laminated body 7, the rigidity of the stator core 2 is increased. Thus, the occurrence of deformation and peeling of the first sheet 6 having a thin sheet thickness is prevented during insertion of the conductor segments 9. When the stator 1 is fixed by being held from first and second axial ends by a frame, the occurrence of warping in outer circumferential portions of the stator core 2 is reliably prevented. Because the rigidity of the stator core 2 is increased, the sheet thickness of the first sheet 6 constituting the laminated body 7 can be reduced. Thus, iron loss which is proportional to the square of the sheet thickness of the steel sheets is reduced, enabling increased efficiency to be achieved in the dynamoelectric machine.
Because opening edge portions of the slots 3 at the first and second axial end surfaces of the stator core 2 are constituted by the chamfered portions 8a of the second sheets 8, damage to the electrically-insulating coating of the conductor segments 9 caused by the burrs 6b is avoided during insertion of the conductor segments 9, during bending or joining of the end portions of the conductor segments 9, and during shaping of coil ends of the stator winding 4 after joining of the conductor segments 9, thereby improving electrical insulation.
In the conventional stator for an automotive alternator, because the stator core 2 is prepared, as described above, by preparing the laminated body 7 by winding the strip-shaped first sheet 6 in which the recess portions 6a (the first slot portions 3a) are formed by press-punching into a helical shape for a predetermined number of winds, preparing the thick annular second sheets 8 in which the second slot portions 3b are formed by press-punching, forming the chamfered portions 8a on the edge portions of the second slot portions 3b of the second sheets 8 by chambering, disposing the faced second sheets 8 at first and second ends of the laminated body 7, and integrating the laminated body 7 and the second sheets 8 by welding, the following problems arise, preventing cost reductions:
First, because the annular second sheets 8 are prepared from a flat magnetic steel sheet material by press-punching, the second sheets 8 cannot be prepared from the magnetic steel sheet material efficiently, increasing the amount of magnetic steel sheet material.
Second, because the chamfered portions 8a are formed on the edge portions of the second slot portions 3b by chambering the annular second sheets 8, slot opening portions are narrow, lowering chambering precision, thereby lowering yield.